1. Field of the Invention
This invention relates to inspection of luggage and other closed containers. More specifically, this invention relates to three-dimensional reconstruction of an image of the inside of closed containers, using scattering of x-rays or other radiant energy.
2. Description of Related Art
Inspection systems for luggage and other closed containers have been commonly used for detecting objects (such as bombs, explosives, weapons, and other contraband) which authorities desire to exclude from entry onto an airplane. Because there are typically very many parcals of luggage to inspect and little time with which to inspect them, these inspection systems must perform their task in a short time and without excessive invasion of the luggage. Existing systems have therefore concentrated on x-ray inspection by review of a projected x-ray image by a human operator.
The following U.S. Pat. Nos.: 4,242,583; 4,277,686; 4,366,382; 4,375,695; 4,495,636; 4,751,722; 4,799,247; 4,825,424; 4,839,913; 4,850,002; 4,870,670; 4,884,289; 4,887,285; and the following articles and books: Kotowski, "New X-Ray Technology to Meet Bomb Threats", Airport Forum, vol. XVII, no. 4 (April 1987); Roder, "Principles, History, and Status of Dual Energy Computerized Tomographic Explosives Detection", Journal of Testing and Evaluation, vol. 13, no. 3 (May 1985); C. Johns, THE PHYSICS OF RADIOLOGY (4th ed. 1983), published by Charles Thomas, comprise at least a partial description of the present state of the art, as known to the inventor.
One problem which has arisen in the art is that the projected x-ray image is only two-dimensional. The two-dimensional image only indicates explosives which may be present by image areas indicating the cumulative density of material which the projected x-ray passes through. While this method may be effective for detecting large solid easily-recognized objects, it is subject to the drawback that true volume density cannot be determined by a projection system; for example, a thin layer of dense material such as metal cannot be distinguished from a thick layer of light material such as clothing.